1. Field of the Invention
This invention relates to lubricating oil compositions, and more particularly to extended service automobile crankcase lubricating oil compositions.
There is a current trend in the automobile industry toward longer intervals between recommended servicing of an automobile. This trend has created a need for crankcase lubricating oils that maintain their effectiveness for periods of four months and longer and for mileage intervals of 6,000 or more. This invention provides a lubricating oil composition which meets these requirements.
2. Prior Art
The automobile crankcase lubricating oil art has been thoroughly developed over the years such that those skilled in the art are able to formulate a lubricating oil composition having a wide variety of properties. The state of this art is well described in a book entitled Motor Oils and Engine Lubrication by Alphonse Schilling, distributed in the U.S. by Scholium International Inc. of Flushing, New York. This book describes in detail the various base stocks and additives which are available, and provides a great deal of information as to the particular properties which can be imported to a composition by addition of one or a combination of the many additives presently available. The Schilling book and U.S. Pat. No. 3,337,456 both describe basic alkaline earth metal sulfonates of the type commonly used as detergents and anti-wear additives. As is well known in the art, the highly basic sulfonates such as overbased magnesium-petroleum sulfonates are commonly used for this purpose.
Another additive commonly used in formulating lubricating oils is an alkaline earth metal phenate sulfide of the type described in the Schilling book and U.S. Pat. No. 2,916,454.
As is known in the art, many additives are multifunctional, and provide beneficial properties of more than one type. Also, most additives have an upper limit beyond which they lead to functional problems as well as being excessively costly. Thus, compositions providing extended service life are not readily attained simply by using higher levels of additives, and any composition which provides extended service life without excessive additive levels is much to be desired.